KR102381947B1 - Laminate sheet and flexible display apparatus comprising same - Google Patents

Abstract

The laminated sheet according to one embodiment has a structure in which a polyester film is laminated on both sides of a transparent substrate, and a certain amount of a UV blocking agent is added to at least one of them, and UV durability and flexibility are adjusted by adjusting the properties and transmittance for each wavelength of each film. This can be improved at the same time. Accordingly, the laminated sheet may be applied to a cover of a flexible display device, particularly a foldable display device, to prevent deterioration in appearance, deformation, or device defects during exposure to UV light and repeated folding due to long-term use.

Description

Laminate sheet and flexible display device including the same

The embodiment relates to a laminated sheet having improved UV durability and flexibility, and a flexible display device including the same.

The display technology is being developed again and again due to the demand according to the development of IT devices, and technologies such as a curved display and a bent display have already been commercialized. Recently, in the field of mobile devices that require both a large screen and portability, a flexible display device that can be flexibly bent or folded according to an external force is preferred. In particular, a foldable display device is a great advantage that it can be folded down when not in use to increase portability, and when not in use, it can be unfolded to realize a large screen.

These flexible display devices mainly use a transparent polyimide film or ultra-thin glass (UTG) as a cover window, but transparent polyimide is vulnerable from external scratches and ultra-thin glass has a weak scattering prevention property. This applies. A film applied to a foldable display device continues to apply a tensile load to the film in a folded state. In this state, when the film is deformed, peeling between the constituent layers may occur.

In order to prevent this, a flexible material that does not easily deform even when a constant load is maintained for a long time, for example, an elastomer-based polymer film may be used as a protective film. However, elastomer-based polymers are difficult to control in process due to their easy-to-stick properties, and it is difficult to manufacture a flawless transparent film due to the generation of gel, which causes a sense of dissimilarity with the cover window. There is a problem that it is easily deformed due to the impact of

Korean Patent Publication No. 2017-0109746

As a protective film applied to a cover of a flexible display device, a polyethylene terephthalate (PET) film is recently considered, but such a polyester film has a weak problem in flexibility required for flexible display applications, that is, elastic recovery ability. In addition, since a general polyester film does not have UV durability, when it is used as a protective film for a display device, yellowing may occur or the performance of the display panel may be impaired by UV light.

On the other hand, if a large amount of a UV blocking agent is added or modified to simply increase the flexibility of the film to solve this problem, the mechanical properties and appearance properties or fairness of the polyester film may be impaired.

As a result of the research conducted by the present inventors, two polyester films are laminated on both sides of a transparent substrate, and a certain amount of UV blocking agent is added to the film to be placed outside the display among them, and a UV blocking agent is added to other films as needed. By controlling the transmittance for each characteristic and wavelength, it was possible to provide a laminated sheet with improved UV durability and flexibility at the same time.

Accordingly, an object of the embodiment is to provide a sheet for a cover in which deformation is suppressed even after exposure to UV light and repeated folding, and a flexible display device including the same.

According to one embodiment, a transparent substrate; a first polyester film disposed on one surface of the transparent substrate; and a second polyester film disposed on the other surface of the transparent substrate, wherein the first polyester film contains (i) 0.5 parts by weight of the UV blocking agent relative to 100 parts by weight of the polyester resin included in the first polyester film. (ii) a total light transmittance of 2% to 5.5% for light of a wavelength of 370 nm, (iii) a total light transmittance of 9.5% to 22% for light of a wavelength of 380 nm, (iv) 390 A laminated sheet is provided, which has a total light transmittance of 65% to 85% for light of a wavelength of nm, and (v) a total light transmittance of 85% to 95% for light of a wavelength of 550 nm.

According to another embodiment, a flexible display panel; and a laminated sheet disposed on the flexible display panel, wherein the laminated sheet includes: a transparent substrate disposed on the display panel; a first polyester film disposed on the transparent substrate; and a second polyester film disposed under the transparent substrate, wherein the first polyester film contains (i) 0.5 parts by weight to 100 parts by weight of the polyester resin included in the first polyester film with a UV blocking agent. Contains 2.0 parts by weight, (ii) 2% to 5.5% of total light transmittance with respect to light of a 370 nm wavelength, (iii) 9.5% to 22% of total light transmittance with respect to light of 380 nm wavelength, (iv) 390 nm wavelength A flexible display device is provided, having a total light transmittance of 65% to 85% with respect to light, and (v) a total light transmittance of 85% to 95% with respect to light having a wavelength of 550 nm.

According to the above embodiment, a certain amount of a UV blocking agent is added to the film to be disposed on the outside of the display among the two polyester films laminated on both sides of the transparent substrate, and a UV blocking agent is added to other films as needed, depending on the characteristics and wavelength of each film. By controlling the transmittance, it is possible to provide a laminated sheet with improved UV durability and flexibility at the same time. Accordingly, the laminated sheet may be applied to a cover of a flexible display device, particularly a foldable display device, to prevent deterioration in appearance, deformation, or device defects during exposure to UV light and repeated folding due to long-term use.

1A and 1B show an example of an in-folding type and an out-folding type display apparatus, respectively.
2A is an exploded perspective view of a cover from the display device.
2B shows an example of a cross-sectional view of a cover of the display device.
3 shows a spectrum of transmittance for each wavelength of light in Examples and Comparative Examples.
4 shows a method of durability testing for repeated folding.
5 shows a method of tensile testing of a polyester film.
6 shows a curve of the tensile rate according to the load applied to the polyester film.
7 and 8 show the curves of the tensile percentage (%) according to time (s) under a constant load condition after UV irradiation of the polyester films of Examples and Comparative Examples, respectively.

In the description of the embodiments below, when one component is described as being formed on or below another component, one component is directly above or below another component, or another component is interposed It includes everything that is formed indirectly by

The size of each component in the drawings may be exaggerated for explanation, and may be different from the size actually applied.

In the present specification, "including" any component means that other components may be further included, rather than excluding other components, unless otherwise stated.

In addition, it should be understood that all numerical ranges indicating physical property values, dimensions, etc. of the components described in the present specification are modified by the term "about" in all cases unless otherwise specified.

In the present specification, unless otherwise specified, the expression “a” is interpreted as meaning including “a” or “plural” as interpreted in context.

Recently, foldable display devices, as shown in FIGS. 1A and 1B , are being developed into an in-folding type (1a) and an out-folding type (1b), and the polyester film applied to the cover 10 of these display devices is heated at room temperature. Since the modulus is large, deformation may occur near the repeatedly folding points p1 and p2. In addition, a general polyester film does not have UV durability, so as shown in FIG. 2a , when it is applied to the cover 10 of the display device, UV light is absorbed by the display panel 20 inside during long-term use, causing problems in driving. can

The embodiment described below is a laminated sheet including a polyester film with improved UV durability and flexibility by controlling the transmittance for a specific wavelength and the strain to a tensile load in a certain range when exposed to UV light, and a flexible including the same A display device is provided.

laminated sheet

As shown in FIGS. 2A and 2B , the cover 10 of the display device 1 is disposed on the display panel 20 , and the adhesive layer 300 is formed on both sides of the transparent substrate 200 in the cover 10 of the display device. Protective films 100a and 100b are laminated through each other. As the cover 10 of such a display device, a sheet in which a polyester film is laminated on both sides of a transparent substrate may be used.

A laminated sheet according to an embodiment includes a transparent substrate; a first polyester film disposed on one surface of the transparent substrate; and a second polyester film disposed on the other surface of the transparent substrate. In the laminated sheet, the first polyester film may include a UV blocking agent, and the second polyester film may or may not include a UV blocking agent.

In addition, the laminated sheet may further include an adhesive layer between the transparent substrate and the first polyester film, and between the transparent substrate and the second polyester film.

The laminated sheet according to the embodiment is advantageous in preventing deformation by protecting internal components from UV light as a cover of the display device.

The laminated sheet may exhibit a transmittance of a specific value or less at wavelengths of 370 nm and 380 nm, and may exhibit a transmittance of a specific value or more at a visible light wavelength such as 390 nm. For example, the laminated sheet may have a total light transmittance of 10% or less, 7% or less, 5% or less, 4.5% or less, or 4% or less for light having a wavelength of 370 nm. In addition, the laminated sheet may have a total light transmittance of 30% or less, 25% or less, 20% or less, 15% or less, or 10% or less with respect to light having a wavelength of 380 nm. As a specific example, the laminated sheet may have a total light transmittance of 5% or less with respect to light of a wavelength of 370 nm and a total light transmittance of 20% or less of light of a wavelength of 380 nm. In addition, the laminated sheet may have a total light transmittance of 45% or more, 50% or more, 55% or more, 60% or more, or 65% or more with respect to light having a wavelength of 390 nm. For example, the laminated sheet may have a total light transmittance of 50% to 90%, 55% to 85%, or 60% to 80% for light having a wavelength of 390 nm. In addition, the laminated sheet may have a total light transmittance of 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more with respect to light having a wavelength of 550 nm. As a specific example, the laminated sheet may have a total light transmittance of 55% or more with respect to light having a wavelength of 390 nm and a total light transmittance of 85% or more with respect to light of a wavelength of 550 nm.

The laminated sheet may have an average rate of change of total light transmittance (%) at a wavelength of 370 nm to 375 nm of 0.1%/nm to 1%/nm, and a rate of change of total light transmittance (%) at a wavelength of 385 nm to 390 nm This average may be 3%/nm to 10%/nm.

The total content of the UV blocking agent in the laminated sheet is 0.5 parts by weight or more, 0.7 parts by weight or more, 0.9 parts by weight or more, 1.1 parts by weight or more, or 1.3 parts by weight, based on 100 parts by weight of the polyester resin included in the laminated sheet. may be more than In addition, the total content of the UV blocking agent in the polyester film is 2.4 parts by weight or less, 2.2 parts by weight or less, 2.0 parts by weight or less, 1.8 parts by weight or less, or It may be 1.6 parts by weight or less. Specifically, the total content of the UV blocking agent included in the first polyester film and the second polyester film is 0.7 compared to 100 parts by weight of the total of the polyester resin in the first polyester film and the second polyester film It may be in an amount of from 2.0 parts by weight to 2.0 parts by weight.

In addition, the number of repeated folding of the laminated sheet under the condition of a curvature radius of 1.5 mm until delamination occurs after 24 hours of irradiation with UV-B light is 100 or more, 1000 or more, 10,000 or more, 50,000 or more, 100,000 times or more or more, 150,000 or more, or 200,000 or more. Specifically, in the polyester film, the number of repeated folding until delamination occurs may be 200,000 or more. When it is within the above range, even when exposed to UV light, deformation does not occur in repeated folding, so that it is advantageously applied to a flexible display device.

When the laminated sheet is applied to a display device, the first polyester film may be located on the front side (outside) and the second polyester film may be located on the back side (inside). That is, as shown in FIGS. 2A and 2B , when the laminated sheet 10 is applied to the display device 1 , the second polyester film 100b may be applied to face the display panel 20 . As such, the first polyester film may be used as a front protective film, and the second polyester film may be used as a rear protective film.

Since the front protective film has to protect the display device from external stimuli, the larger the thickness, the more advantageous. On the other hand, since the back protective film is not directly stimulated from the outside, it is okay to have a thin thickness, and in a thin thickness, flexibility may not be significantly impaired even if the modulus is higher than a certain level.

Accordingly, the laminated sheet may satisfy Equations (1) and (2) below.

1.5 ≤ T1/T2 ... (1) 0.8 ≤ M2/M1 ≤ 1.2 ... (2)

Wherein T1 is the thickness of the first polyester film, T2 is the thickness of the second polyester film, M1 is the modulus (GPa) with respect to the width direction (TD) of the first polyester film, M2 is The modulus (GPa) with respect to the width direction (TD) of the second polyester film.

The T1/T2 may be 1.5 or more, 2.0 or more, 2.5 or more, or 3.0 or more, for example, 1.5 to 5.0, or 2.0 to 4.0. As an example, the T1 may be 45 μm to 80 μm, and the T2 may be 10 μm to 30 μm. The M2/M1 may be 0.8 or more, 1.0 or more, more than 1.0, 1.05 or more, or 1.1 or more, and may be 1.2 or less, or 1.15 or less, for example, 1.05 to 1.2.

first and second polyester films

The first polyester film and the second polyester film include a polyester resin.

The polyester resin may be a homopolymer resin or a copolymer resin in which dicarboxylic acid and diol are polycondensed. In addition, the polyester resin may be a blend resin in which the homopolymer resin or copolymer resin is mixed.

Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5- Naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclo Hexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2 ,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid trimethyladipic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, dodecadicarboxylic acid, and the like.

In addition, examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, and the like.

Preferably, the polyester resin may be an aromatic polyester resin having excellent crystallinity, and for example, a polyethylene terephthalate (PET) resin may be a main component.

As an example, the polyester film may include about 85% by weight or more of a polyester resin, specifically, a PET resin, and more specifically, 90% by weight or more, 95% by weight or more, or 99% by weight or more. As another example, the polyester film may further include another polyester resin in addition to the PET resin. Specifically, the polyester film may further include a polyethylene naphthalate (PEN) resin in an amount of about 15% by weight or less. More specifically, the polyester film may further include about 0.1 wt% to 10 wt%, or about 0.1 wt% to 5 wt% of PEN resin.

According to the composition, the degree of crystallinity may increase in a manufacturing process in which the polyester film undergoes heating, stretching, etc., and mechanical properties such as tensile strength may be improved.

The first polyester film includes a UV blocking agent, and the second polyester film includes or does not include a UV blocking agent.

As an example, both the first polyester film and the second polyester film may include a UV blocking agent. In this case, the content of the UV blocking agent in the first polyester film or the second polyester film is 0.5 parts by weight or more, 0.7 parts by weight or more, 0.9 parts by weight, based on 100 parts by weight of the polyester resin included in each polyester film. parts by weight or more, 1.1 parts by weight or more, or 1.3 parts by weight or more. In addition, the content of the UV blocking agent in the first polyester film or the second polyester film is 2.4 parts by weight or less, 2.2 parts by weight or less, 2.0 parts by weight or less, relative to 100 parts by weight of the polyester resin included in each polyester film parts by weight or less, 1.8 parts by weight or less, or 1.6 parts by weight or less.

As another example, the second polyester film may include no or a trace amount of a UV blocker, in which case the content of the UV blocker in the second polyester film is 100 of the polyester resin included in the second polyester film. It may be less than 0.5 parts by weight, or less than 0.1 parts by weight relative to parts by weight.

According to one embodiment, the UV blocking agent content in the first polyester film is 0.5 parts by weight to 2.0 parts by weight based on 100 parts by weight of the polyester resin included in the first polyester film. In addition, the UV blocker content in the second polyester film may be less than 0.1 parts by weight compared to 100 parts by weight of the polyester resin included in the second polyester film.

On the other hand, if the UV blocking agent does not have sufficient heat resistance, it may be mixed into the polyester resin and decomposed in a significant amount during extrusion at high temperature, which may adversely affect the UV blocking property of the film. Accordingly, it is preferable that the UV blocking agent has a weight reduction rate of the polyester resin at a melting temperature of a certain level or less. For example, the UV blocking agent is maintained for 1 hour in an air atmosphere at 280 ° C. The weight loss may be 20% or less, 15% or less, or 10% or less. Specifically remind The UV blocking agent may have a weight reduction rate of 15% or less after maintaining for 1 hour in an air atmosphere at 280° C. under isothermal conditions of a thermogravimetric analyzer (TGA). More specifically, the weight reduction rate may be 1% to 15%, 5% to 15%, or 10% to 15%.

The specific type of the UV blocker is not particularly limited, but for example, at least one UV blocking agent selected from the group consisting of a benzophenone type, a benzotriazole type, a triazine type, a malonic acid ester type, a benzoate type, and a benzoxazinone type. can be the best

As an example, the UV blocker may be a benzoxazinone-based UV blocker, and specifically, may have one or more benzoxazinone groups, and more specifically, two benzoxazinones linked through an unsaturated hydrocarbon ring or an aromatic ring. You can have groups.

As an example, the UV blocking agent may be one or more compounds having a structure of Formula 1 below:

[Formula 1]

In the above formula, R ₁ and R ₂ are each independently hydrogen, alkyl, or alkenyl, and L is a single bond or a hydrocarbon chain, hydrocarbon ring or heterocycle having one or more unsaturated bonds.

The alkyl may be an alkyl having 1 to 6 carbon atoms, and the alkenyl may be an alkenyl having 2 to 6 carbon atoms. The hydrocarbon chain may have 2 to 10 carbon atoms, the hydrocarbon ring may have 6 to 20 carbon atoms, and the hetero ring is a 5 to 20 membered ring containing one or more heteroatoms selected from N, S and O can be In addition, the hydrocarbon ring or hetero ring may be an aromatic ring, for example, the hydrocarbon ring may be a benzene ring, the hetero ring may be a pyridine ring.

The L may be a group forming a conjugation structure with two benzooxazinone groups connected thereto.

The polyester film including the UV blocking agent is applied to the cover of the display device to protect the internal components from UV light and is advantageous in preventing deformation.

3 shows a spectrum of transmittance for each wavelength of light in Examples and Comparative Examples. As shown in FIG. 3 , both the Example and the comparative example show generally low transmittance in the UV wavelength band, but it can be seen that there is a difference in the curves of the Example and the comparative example in terms of transmittance at a specific wavelength.

Specifically, the curve of the example maintains a very low transmittance until the end of the UV region (eg, 370 nm), and then the transmittance rapidly increases from the boundary point (eg, 380 nm), so that it is already at the beginning of the visible light region (eg, 390 nm). It shows a considerable level of transmittance. On the other hand, the curve of the comparative example shows a level of transmittance at the boundary point (eg 380 nm) as the transmittance gradually increases from before the end of the UV region (eg 370 nm), and up to the beginning of the visible light region (eg 390 nm). It shows a gradual rise. As such, the polyester film may exhibit a transmittance of a specific value or less at wavelengths of 370 nm and 380 nm, and may exhibit a transmittance of a specific value or more at a visible light wavelength such as 390 nm.

For example, the polyester film may have a total light transmittance of 10% or less, 7% or less, 5.5% or less, 5% or less, 4.5% or less, or 4% or less for light having a wavelength of 370 nm. Specifically, the polyester film may have a total light transmittance of 5% or less for light having a wavelength of 370 nm. In addition, the polyester film may have a total light transmittance of 30% or less, 25% or less, 22% or less, 20% or less, 15% or less, or 10% or less for light having a wavelength of 380 nm. In addition, the polyester film may have a total light transmittance of 45% or more, 50% or more, 55% or more, 60% or more, or 65% or more for light having a wavelength of 390 nm. For example, the polyester film may have a total light transmittance of 50% to 90%, 55% to 85%, or 60% to 80% for light having a wavelength of 390 nm. In addition, the polyester film may have a total light transmittance of 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more for light having a wavelength of 550 nm.

According to one embodiment, the first polyester film has a total light transmittance of 2% to 5.5% for light of a wavelength of 370 nm, a total light transmittance of 9.5% to 22% for light of a wavelength of 380 nm, light of a wavelength of 390 nm It has a total light transmittance of 65% to 85%, and a total light transmittance of 85% to 95% for light having a wavelength of 550 nm. When within the above range, the laminated sheet including the first polyester film is advantageous in preventing deformation by protecting internal components from UV light as a cover of the display device.

In addition, the first polyester film may have an average rate of change of total light transmittance (%) at a wavelength of 370 nm to 375 nm of 0.1%/nm to 1%/nm, and total light transmittance at a wavelength of 385 nm to 390 nm ( %) may have an average change rate of 3%/nm to 10%/nm.

In addition, even after the first polyester film is exposed to UV light, the strain with respect to the tensile load is adjusted in a certain range. Accordingly, the laminated sheet including the first polyester film may be applied to the cover of the flexible display device to maintain original characteristics during repeated folding even when exposed to external UV light. The UV light may be, for example, UV-B light, and a specific wavelength range of the UV-B light may be about 280 nm to 315 nm. Specifically, the UV-B light has a peak wavelength within 310 nm to 315 nm, and an irradiance at a wavelength of 310 nm is about 0.66 W/m ² (eg, 0.6 to 0.7 W/m ² ), The total irradiation amount in the 250 nm to 400 nm wavelength band may be about 31.62 W/m ² (eg, 31.6 to 31.7 W/m ² ).

According to one embodiment, the first polyester film, after 24 hours of irradiation of UV-B light, a final tensile rate of 3% or less at a time duration of 1 hour with a load of N2% with respect to the in-plane first direction. Here, the N2% load is a load that stretches the film in the first direction by 2% compared to the initial load. Specifically, the tensile rate may be measured at room temperature with an initial dimension of 50 mm (initial distance between points to which a tensile load is applied) of the film in the first direction and a dimension of 15 mm in a direction perpendicular thereto.

More specifically, the first polyester film is (1) a film having an initial dimension of 50 mm in a first direction in-plane and a dimension of 15 mm in a direction perpendicular thereto, when the film is stretched in the first direction, the dimension is 1 compared to the initial dimension After measuring the load (N2%) at the time of % increase, (2) the ratio of the increased dimension to the initial dimension of the film when the load (N2%) is continuously applied for 1 hour in the first direction of the film, that is, The final tensile rate is 3% or less.

As an example, the first polyester film may have a final tensile rate of 3% or less, 2.7% or less, 2.5% or less, or 2.3% or less after 24 hours of irradiation of UV-B light with a load of N2% for 1 hour. there is. For example, the film has a final tensile rate of 1.5% to 3%, respectively, in the first and second directions perpendicular to each other in-plane after 24 hours of irradiation with UV-B light at the N2% load for 1 hour. , 2% to 3%, 2.3% to 3%, 2% to 2.7%, or 2% to 2.5%. Specifically, the film has a final tensile rate for 1 hour under a load of N2% after 24 hours of UV-B light irradiation, 2% to 3%, respectively, for the first and second directions perpendicular to each other in-plane can

As another example, the first polyester film may have a final tensile rate of 2% or less when irradiated with UV-B light for 24 hours under a load of N1% in the in-plane first direction for 1 hour. Here, the N1% load is a load that stretches the film in the first direction by 1% compared to the initial load. For example, the film may have a final tensile rate of 1.7% or less, 1.5% or less, or 1.3% or less when irradiated with UV-B light for 24 hours and maintained for 1 hour under a load of N1%. Specifically, the film has a final tensile rate for 1 hour under a load of N1% after 24 hours of irradiation with UV-B light, 1.1% to 2%, respectively, for the first and second directions perpendicular to each other in-plane, 1.3% to 2%, 1.5% to 2%, 1.1% to 1.7%, or 1.1% to 1.5%. The tensile rate may be measured at room temperature with an initial dimension of 50 mm in the first direction and 15 mm in a direction perpendicular thereto.

As another example, the first polyester film may have a final tensile rate of 7% or less when irradiated with UV-B light for 24 hours under a load of N3% in the in-plane first direction for 1 hour. Here, the N3% load is a load that stretches the film in the first direction by 3% compared to the initial load. For example, the film has a final tensile rate of 6.7% or less, 6.5% or less, 6.3% or less, 6% or less, or 5.7% after 24 hours of irradiation of UV-B light with a load of N3%. may be below. Specifically, the film has a final tensile rate for 1 hour with a load of N3% after 24 hours of UV-B light irradiation, 3% to 7%, respectively, for the first and second directions perpendicular to each other in-plane, 5% to 7%, 5% to 6%, 5.5% to 6.5%, or 6% to 7%. The tensile rate may be measured at room temperature with an initial dimension of 50 mm in the first direction and a dimension of 15 mm in a direction perpendicular thereto.

As a specific example, after the first polyester film is irradiated with UV-B light for 24 hours, the final tensile rate is 2% or less at a time of 1 hour under a load of N1% with respect to the in-plane first direction, and the in-plane first direction The final tensile rate may be 7% or less when lasting for 1 hour with a load of N3%. Here, the loads of N1% and N3% are loads that stretch the film by 1% and 3%, respectively, in the first direction compared to the initial load.

In addition, the second polyester film may also have the same tensile properties as the first polyester film.

The first direction may be any direction in-plane of the film, and the second direction may be determined as a direction perpendicular to the first direction in-plane. For example, the first direction may be a longitudinal direction (MD) or a width direction (TD) of the film, and the second direction may be a width direction (TD) or a longitudinal direction (MD) perpendicular thereto. Specifically, the first direction may be a longitudinal direction (MD) of the film, and the second direction may be a width direction (TD) of the film.

6 shows a curve of the tensile rate (%) according to the load (N) applied to the polyester film. The loads of N1%, N2%, and N3% may be determined from the tensile rate curve according to the load, respectively. Specifically, in the polyester film, the load of N1% may be 28 N to 32 N, the load of N2% may be 50 N to 55 N, and the load of N3% may be 64 N to 68 N. can

7 and 8 show the curves of the tensile percentage (%) according to time (s) under a constant load condition after UV irradiation of the polyester films of Examples and Comparative Examples, respectively. As such, the polyester film of the embodiment has a final tensile rate of 2% or less when the N1% load is applied for 1 hour, and a final tensile rate of 3% or less when the N2% load is applied for 1 hour or less, and the N3 While the final tensile rate at a time duration of 1 hour with a load of % was 7% or less, the polyester film of Comparative Example was out of the above tensile property range.

A ratio of the N2% load and the N1% load may be 1.6:1 to 2.1:1. Specifically, the ratio of the N2% load and the N1% load may be 1.75:1 to 1.95:1. In addition, the ratio of the N3% load and the N2% load may be 1.2:1 to 1.5:1. Specifically, the ratio of the N3% load and the N2% load may be 1.20:1 to 1.35:1.

The first and second polyester films are preferably biaxially stretched in terms of flexibility and elastic recovery. In this case, the ratio between the respective draw ratios for the biaxial may be 1:0.5 to 1:1.5, 1:0.7 to 1:1.3, or 1:0.8 to 1:1.2. Specifically, the first and second polyester films are biaxially stretched, and the ratio between the respective draw ratios for the biaxially may be 1:0.8 to 1:1.2. When the draw ratio is within the range, it may be more advantageous to have flexibility in which deformation does not occur even when a constant load is continued for a long time.

The first and second polyester films may be biaxially stretched in a first in-plane direction and in a second in-plane direction perpendicular to the first direction. In this case, the first direction stretching ratio may be 2.0 to 5.0, specifically 2.8 to 3.5, or 3.3 to 3.5. In addition, the stretch ratio in the second direction may be 2.0 to 5.0, specifically 2.9 to 3.7, or 3.5 to 3.8. Specifically, the first and second polyester films may be biaxially stretched at a longitudinal stretch ratio of 3.3 to 3.5, and a transverse stretch ratio of 3.5 to 3.8. In addition, the ratio (d2/d1) of the second direction draw ratio (d2) to the first direction draw ratio (d1) may be 1.2 or less, for example, 1.0 to 1.2, 1.0 to 1.1, 1.0 to 1.15, or 1.05 to It can be 1.1.

The thickness of the first polyester film and the second polyester film is each 10 μm to 500 μm, 10 μm to 300 μm, 10 μm to 100 μm, 10 μm to 80 μm, 20 μm to 80 μm, 30 μm to 80 μm, 40 μm to 60 μm, or 10 μm to 30 μm. As an example, when the first polyester film and the second polyester film are respectively applied as front and rear protective films of the cover, the first polyester film has a thickness of 20 μm to 80 μm, specifically 60 μm to 80 μm. may have, and the second polyester film may have a thickness of 30 μm or less, specifically 10 μm to 30 μm.

transparent substrate

The transparent substrate may be a cover window of the display device.

The transparent substrate may be a polymer film or a glass substrate. Specifically, the transparent substrate may be a transparent polyimide film or ultra-thin glass (UTG).

As an example, the transparent substrate may include a polyimide-based resin. Specifically, the transparent cover may be a polyimide-based film.

The polyimide-based film includes a polyimide-based polymer, and the polyimide-based polymer is formed by polymerizing a diamine compound, a dianhydride compound, and optionally a dicarbonyl compound.

The polyimide-based polymer is a polymer including an imide repeating unit. In addition, the polyimide-based polymer may optionally include an amide repeating unit. The polyimide-based polymer may be formed by simultaneously or sequentially reacting reactants including a diamine compound and a dianhydride compound. Specifically, the polyimide-based polymer is formed by polymerization of a diamine compound and a dianhydride compound. Alternatively, the polyimide-based polymer may be formed by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound. In this case, the polyimide-based polymer includes an imide repeating unit derived from polymerization of a diamine compound and a dianhydride compound and an amide repeating unit derived from polymerization of the diamine compound and a dicarbonyl compound.

The diamine compound may be, for example, an aromatic diamine compound having an aromatic structure. Specifically, the diamine compound may include 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB), but is not limited thereto.

The dianhydride compound may be an aromatic dianhydride compound having an aromatic structure or an alicyclic dianhydride compound having an alicyclic structure. Specifically, the dianhydride compound may include 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), but is not limited thereto.

The dicarbonyl compound may be an aromatic dicarbonyl compound having an aromatic structure. The dicarbonyl compound may include terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC), isophthaloyl chloride (IPC), or a combination thereof. However, the present invention is not limited thereto.

The diamine compound and the dianhydride compound may be polymerized to produce a polyamic acid. Subsequently, the polyamic acid may be converted into polyimide through a dehydration reaction, and the polyimide includes an imide repeating unit.

For example, the polyimide may include a repeating unit represented by the following Chemical Formula A-1, but is not limited thereto.

<Formula A-1>

In Formula A-1, n is, for example, an integer of 1 to 400.

In addition, the diamine compound and the dicarbonyl compound may be polymerized to form an amide repeating unit represented by Formulas B-1 to B-3.

<Formula B-1>

In Formula B-1, x is, for example, an integer of 1 to 400.

<Formula B-2>

In Formula B-2, y is, for example, an integer of 1 to 400.

<Formula B-3>

In Formula B-3, y is, for example, an integer of 1 to 400.

The thickness of the transparent substrate may be 20 μm to 500 μm, 30 μm to 300 μm, or 40 μm to 100 μm.

The transparent substrate may have a surface hardness of HB or more and a light transmittance of 80% or more at a wavelength of 550 nm. In addition, the transparent substrate may have a yellowness of 5 or less and a haze of 2% or less based on a thickness of 50 μm.

The transparent substrate may have a strain of 10% or more, 12% or more, 15% or more, or 20% or more until whitening occurs. When it is within the above range, the whitening phenomenon does not occur even when it is deformed due to frequent folding, so that it is advantageously applied to a flexible display device. The strain refers to a ratio of a changed dimension to an original dimension of the film, wherein the changed dimension may be an increased dimension or a decreased dimension. In particular, both the protective film and the transparent substrate may have a strain of 10% or more until whitening occurs.

adhesive layer

The laminated sheet may further include an adhesive layer between the transparent substrate and the first polyester film, and between the transparent substrate and the second polyester film.

The thickness of the adhesive layer may be 1 μm to 50 μm, 3 μm to 30 μm, 5 μm to 20 μm, 5 μm to 15 μm, 7 μm to 12 μm, or 8 μm to 12 μm.

Specifically, the first adhesive layer and the second adhesive layer may have a thickness of 5 to 15 μm. When it is within the preferred thickness range, it may be more advantageous to suppress curl while having excellent interfacial adhesion.

The first adhesive layer and the second adhesive layer may include an adhesive resin, and may further include a curing agent and/or a photoinitiator.

The adhesive resin is not particularly limited, but may be, for example, a resin that can be cured by UV light irradiation, and thus the first adhesive layer and the second adhesive layer may be manufactured through UV curing. In addition, the adhesive resin may be a resin that is not yellowed by UV light and has good dispersibility of the UV absorber. For example, the adhesive resin may include a polyester resin, an acrylic resin, an alkyd resin, and an amino resin. The adhesive resin may be used alone, or two or more types of copolymers or mixtures may be used. Among them, an acrylic resin excellent in optical properties, weather resistance, adhesion to a substrate, and the like is preferable. In addition, the adhesive resin may be an optical clear adhesive (OCA).

The curing agent is not particularly limited as long as it is a material capable of curing the adhesive resin. Specifically, one or more may be selected from the group consisting of an isocyanate curing agent that does not yellow by UV light, an epoxy curing agent, and an aziridine curing agent. In addition, the curing agent may be included in an amount of 0.2 to 0.5% by weight, 0.3 to 0.5% by weight, 0.3 to 0.45% by weight, or 0.35 to 0.45% by weight based on the weight of each of the first and second adhesive layers.

The photoinitiator is required for UV curing, for example, benzophenone-based, thioxanthone-based, α-hydroxy ketone-based, ketone-based, phenyl glyoxylate At least one type may be selected from the group consisting of (phenyl glyoxylate)-based and acyl phosphine oxide-based. The photoinitiator may be included in an amount of 0.1 to 5.0% by weight based on the weight of each of the first and second adhesive layers.

coating layer

The laminated sheet may further include one or more coating layers disposed on the polyester film.

The coating layer may be disposed between the polyester film and the transparent substrate, or disposed on the outer surface of the protective film.

The coating layer may be a functional coating layer for hardness improvement, antistatic, scattering prevention, refractive index control, surface protection, and the like.

Manufacturing method of laminated sheet

The lamination sheet may be manufactured by a method of laminating a polyester film on both sides of a transparent substrate using an adhesive after manufacturing the polyester film.

A method of manufacturing a laminated sheet according to an embodiment comprises the steps of preparing a first polyester film and a second polyester film; forming an adhesive layer on one surface of the first polyester film and the second polyester film; and laminating the first polyester film and the second polyester film on which the adhesive layer is formed on one surface and the other surface of the transparent substrate, respectively.

The first and second polyester films may be prepared by a process including biaxial stretching and heat treatment at a specific temperature with a controlled stretch ratio using a resin composition. At this time, a UV blocking agent may be added to the resin composition, and the amount thereof may be adjusted as exemplified above. In particular, the method for producing the first and second polyester films includes forming a film with a resin composition, biaxially stretching and heat-treating, and obtaining a film having a final tensile rate of 3% or less when lasting 1 hour under a load of N2% includes In this case, the composition and process conditions are adjusted so that the film finally manufactured by the above method satisfies the tensile properties described above. Specifically, in order for the final film to satisfy the above characteristics, the extrusion and casting temperature of the polyester resin is adjusted, the preheating temperature during stretching, the stretching ratio for each direction, the stretching temperature, the moving speed, etc. are adjusted, or heat treatment after stretching And while performing relaxation, it is possible to control the heat treatment temperature and the relaxation rate.

Hereinafter, each step for producing the polyester film will be described in more detail.

First, the resin composition is melted and extruded to be cast into a film. The extrusion may be performed at a temperature of 230°C to 300°C, or 250°C to 280°C.

The film may be preheated at a predetermined temperature before stretching. The range of the preheating temperature satisfies the range of Tg+5℃ to Tg+50℃ based on the glass transition temperature (Tg) of the polyester resin, and at the same time, it is determined to be a range that satisfies the range of 70℃ to 90℃ can When it is within the above range, it is possible to effectively prevent the film from breaking during stretching while securing flexibility for easy stretching of the film.

The stretching is carried out by biaxial stretching, for example, it can be stretched biaxially in the longitudinal direction (i.e. machine direction) (MD) and in the width direction (i.e. tenter direction) (TD) through a simultaneous biaxial stretching method or a sequential biaxial stretching method. there is. Preferably, a sequential biaxial stretching method of stretching in one direction first and then stretching in a direction perpendicular to the direction may be performed. The stretching speed may be 6.5 m/min to 8.5 m/min, but is not particularly limited.

The lengthwise stretch ratio may be 2.0 to 5.0, specifically 2.8 to 3.5, or 3.3 to 3.5. In addition, the width direction stretch ratio may be 2.0 to 5.0, specifically 2.9 to 3.7, or 3.5 to 3.8. When it is within the above preferred range, it may be more advantageous to uniform the thickness. In addition, it is preferable to adjust the load applied during stretching in each direction so that the difference in refractive index in each direction is minimized while measuring the refractive index in order to balance the longitudinal direction MD and the width direction TD. In addition, the ratio (d2/d1) of the stretch ratio in the width direction (d2) to the stretch ratio in the longitudinal direction (d1) may be 1.2 or less, for example, 1.0 to 1.2, 1.0 to 1.1, 1.0 to 1.15, or 1.05 to 1.1. there is. The said draw ratios (d1, d2) are ratios which show the length after extending|stretching, when the length before extending|stretching is made into 1.0.

Thereafter, the stretched film is subjected to a heat treatment step. The heat treatment may be performed at a temperature of 180 °C or higher, specifically 195 °C or higher, and more specifically 195 °C to 230 °C. The heat treatment may be performed for 0.2 minutes to 1 minute, and more specifically, may be performed for 0.4 minutes to 0.7 minutes.

In addition, after starting the heat treatment, the film may be relaxed in the longitudinal direction and/or the width direction, and the temperature range at this time may be 150°C to 250°C. The relaxation may be performed at a relaxation rate of 1% to 10%, 2% to 7%, or 3% to 5%. In addition, the relaxation may be performed for 1 second to 1 minute, 2 seconds to 30 seconds, or 3 seconds to 10 seconds.

In addition, the film may be cooled after the heat treatment, and the cooling may be performed at a temperature lower than 50° C. to 150° C. compared to the heat treatment temperature.

The first and second polyester films prepared in this way may be laminated on both sides of the transparent substrate after the adhesive is applied on one surface.

flexible display device

The flexible display device according to an exemplary embodiment includes the above-described laminated sheet in a cover. That is, the flexible display device may include a flexible display panel; and the laminated sheet disposed on the flexible display panel.

The laminated sheet included in the flexible display device has substantially the same configuration and characteristics as the above-described laminated sheet. Specifically, the laminated sheet may include a transparent substrate disposed on the display panel; a first polyester film disposed on the transparent substrate; and a second polyester film disposed under the transparent substrate, wherein the first polyester film contains (i) 0.5 parts by weight to 100 parts by weight of the polyester resin included in the first polyester film with a UV blocking agent. Contains 2.0 parts by weight, (ii) 2% to 5.5% of total light transmittance with respect to light of a 370 nm wavelength, (iii) 9.5% to 22% of total light transmittance with respect to light of 380 nm wavelength, (iv) 390 nm wavelength It has a total light transmittance of 65% to 85% for light, and (v) a total light transmittance of 85% to 95% for light of a wavelength of 550 nm.

According to the embodiment, a UV blocking agent is added to at least one of the two polyester films provided in the laminated sheet to prevent deterioration in appearance, deformation or device defects when exposed to UV light due to long-term use. can

The flexible display device may be a foldable display device. Specifically, the foldable display device may be an in-folding type or an out-folding type according to a folding direction. 1A and 1B, the foldable display device may be of an in-folding type (1a) in which the screen is positioned inside the folding direction and an out-folding type (1b) in which the screen is positioned outside in the folding direction. there is.

In a material applied to a flexible display device, a property that is as important as flexibility is that the original property does not deteriorate even after frequent bending or folding. Since it is almost impossible to return to the original shape due to the fact that a general material is completely folded and unfolded, it is almost impossible to return to its original shape.

Specifically, with reference to FIG. 1A , in the case of the in-folding type 1a, due to the deformation due to the load applied to the inward folding point p1, and also referring to FIG. 1B, in the case of the out-folding type 1b Whitening or cracks may occur in the cover 10 due to deformation due to a load occurring at the outwardly folding point p2, and thus properties may be easily deteriorated. Such whitening and cracking can be generally solved when the modulus of the protective film is low at room temperature, but a cover having a conventional polyester film generally has a large modulus at room temperature, so whitening and cracking when applied to a flexible display device There are problems that arise easily.

However, the laminated sheet according to the embodiment can implement the flexibility required for the cover of the flexible display because the mechanical properties of the constituent layers including the polyester film provided therein are adjusted to a specific range even in a UV exposure environment, and as a result, the embodiment The laminated sheet according to the present invention may be applied to the cover of the flexible display device to maintain original characteristics even during multiple repeated folding.

In the flexible display device, the flexible display panel may be, specifically, an organic light emitting display (OLED) panel. 9 is a cross-sectional view schematically illustrating an example of an organic light emitting display device 1 ′ including an organic light emitting display panel 20 - 2 . Referring to FIG. 9 , the organic light emitting display device 1 ′ includes a front polarizing plate 20 - 1 and an organic light emitting display panel 20 - 2 . The front polarizing plate may be disposed on the front surface of the organic light emitting display panel. More specifically, the front polarizing plate may be adhered to a surface on which an image is displayed in the organic light emitting display panel. The organic light emitting display panel displays an image by self-luminescence in units of pixels. The organic light emitting display panel includes an organic light emitting substrate and a driving substrate. The organic light emitting substrate includes a plurality of organic light emitting units respectively corresponding to pixels. Each of the organic light emitting units includes a cathode, an electron transport layer, a light emitting layer, a hole transport layer, and an anode. The driving substrate is drivably coupled to the organic light emitting substrate. That is, the driving substrate may be coupled to apply a driving signal such as a driving current to the organic light emitting substrate. More specifically, the driving substrate may drive the organic light emitting substrate by applying current to each of the organic light emitting units.

Hereinafter, more specific embodiments will be described, but the scope of implementation is not limited thereto.

Evaluation example of UV blocker

Thermogravimetric analyzer (TGA) evaluation was performed to select a UV blocker with excellent processing efficiency even at the processing temperature of polyethylene terephthalate (PET) resin. The suitability of the UV blocker was judged as PASS if the weight loss did not exceed 15% after maintaining for 1 hour under an isothermal condition of 280°C under an air atmosphere using Q500 equipment from TA Instruments, and FAIL otherwise.

division designation TGA evaluation result UV Blocker 1 Benzophenone-3 FAIL UV Blocker 2 Phenol, 2-(2H-benzotriazol-2-yl)-4-methyl FAIL UV Blocker 3 2,2'-(1,4-Phenylene)bis(4H-3,1-benzoxazin-4-one) PASS

Preparation example of polyester film

A composition in which a UV blocking agent as shown in the following table was added to a polyethylene terephthalate (PET) resin as shown in Table 2 below was extruded at 280° C. and then cast in a film shape through a T-die. The cast film was preheated at 100° C. and stretched 3.0 times in the longitudinal direction (MD) and 3.3 times in the transverse direction (TD). At this time, the extending|stretching temperature was made into 130 degreeC. Thereafter, the stretched film was heat-set at 200° C., relaxed 3%, and then cooled to prepare a polyester film having a thickness of 60 μm. In addition, as a comparative example, a polyester film was prepared in the same manner as before without adding a UV blocking agent.

division PET resin composition Types of UV Blockers UV blocker content (parts by weight) film A1 Comparative Example 1 - - film A2 Comparative Example 2 UV Blocker 1 1.3 film B1 Example 1 UV Blocker 3 1.1 film B2 Example 2 UV Blocker 3 1.6 film B3 Example 3 UV Blocker 3 0.9 film B4 Example 4 UV Blocker 3 0.8 film B5 Example 5 UV Blocker 3 0.8 * UV blocker content: parts by weight of solid content of UV blocker added per 100 parts by weight of PET resin

Experimental example of total light transmittance

The total transmittance was measured for the polyester film sample as follows.

- Measuring equipment: Hunterlab's Ultrascan pro Colorimeter

- Measurement procedure: ASTM D1003

- Light source: D65/10

- Diffusion angle: 8°

The results are shown in the table below.

division Total light transmittance (%) 370 nm 380 nm 390 nm 550 nm film A1 Comparative Example 1 75 81 87.8 93.2 film A2 Comparative Example 2 5.8 18.5 72.1 92.9 film B1 Example 1 3.81 11.5 70.7 93.2 film B2 Example 2 3.5 9.7 71.3 92.9 film B3 Example 3 3.9 16.5 68.7 92.9 film B4 Example 4 3.98 19.1 70.9 93.1 film B5 Example 5 3.97 19.6 71.1 93.2

Experimental example of tensile rate

The tensile rate was measured for the polyester film. Referring to FIG. 5 , four rectangular specimens 101 adjacent to each other at a distance w of 15 mm in the polyester film 100 are cut, and the specimen 101 is placed on the jig 21 of the test equipment 2 . ) was fixed at both ends. Thereafter, the tensile rate was measured according to the following conditions and procedures.

- initial dimension in tension direction 50 mm

- dimension in the direction perpendicular to the direction of tension 15 mm

- Test temperature: room temperature (25℃)

- Test equipment: Instron's UTM 5566A

- Tensile speed: 50 mm/min

- Tensile direction: length direction (MD) or width direction (TD) of the polyester film

(1) Measurement of load by initial tensile rate

First, each load that stretches the specimen by 1%, 2%, or 3% relative to its initial dimension was first measured.

(2) Measurement of the final tensile rate under continuous load

Then, after maintaining the previously measured load to be applied to the specimen uniformly for 1 hour, the final tensile rate (%) compared to the initial specimen dimension was measured.

(3) The procedure of (1) and (2) above was performed for 4 specimens, and the average value was taken. The results are summarized in the table below.

Experimental example of tensile rate after UV irradiation

The tensile rate was measured after UV irradiation under the following conditions.

(a) UV irradiation

- UV equipment: Q-lab's QUV Tester

- UV lamp: UVB-313

- UV dose: 0.66 W/m ² @310 nm

- UV total dose: 31.62 W/m ² @250-400 nm

- UV irradiation time: 24 hours

(b) The tensile rate of the UV-irradiated specimen was measured in the same manner as before.

The results are summarized in the table below.

division Early
tensile rate
(%) Tensile rate (%) after 1 hour Before UV-B irradiation After UV-B irradiation MD TD MD TD film A1 Comparative Example 1 One 1.2 1.21 1.67 2.11 2 2.4 2.38 3.1 3.57 3 5.80 5.91 7.13 7.9 film A2 Comparative Example 2 One 1.33 1.41 1.71 1.99 2 2.15 2.67 2.81 3.21 3 4.97 5.93 6.37 7.13 film B1 Example 1 One 1.11 1.15 1.17 1.21 2 2.37 2.69 2.38 2.66 3 5.11 6.7 5.36 6.91 film B2 Example 2 One 1.31 1.32 1.31 1.35 2 2.48 2.91 2.49 2.91 3 5.31 6.72 5.33 6.71 film B3 Example 3 One 1.16 1.17 1.23 1.25 2 2.31 2.67 2.47 2.82 3 4.09 5.11 4.66 5.93 film B4 Example 4 One 1.16 1.23 1.19 1.24 2 2.3 2.35 2.53 2.78 3 4.6 5.7 5.21 6.37 film B5 Example 5 One 1.11 1.18 1.21 1.67 2 2.2 2.45 2.57 2.91 3 5.31 6.21 6.27 6.91

Manufacturing example of laminated sheet

A film having a thickness of 60 μm prepared in the same manner as in the polyester films A1 to B5 was prepared, respectively, and was used as a first polyester film. In addition, a film having a thickness of 15 to 20 μm was prepared without including a UV blocker prepared in the same manner as in film A1, and was used as a second polyester film. An optically clear adhesive (OCA) was coated on one side of the first polyester film and one side of the second polyester film to a thickness of 10 μm, respectively, and laminated on both sides of the cover window. A transparent polyimide film (see Preparation Example below) having a thickness of 50 μm was used as the cover window. As a result, the laminated sheet which has the structure of 1st polyester film/OCA layer/cover window/OCA layer/2nd polyester film was obtained.

division first polyester film 2nd polyester film Manufacturing method UV blocker
content Thickness (㎛) UV blocker
content Thickness (㎛) sheet A1 Comparative Example 1 film A1 0 60 0 20 sheet A2 Comparative Example 2 film A2 1.3 60 0 20 sheet B1 Example 1 film B1 1.1 60 0 20 sheet B2 Example 2 film B2 1.6 60 0 15 sheet B3 Example 3 film B3 0.9 60 0 15 sheet B4 Example 4 film B4 0.8 60 0 17 sheet B5 Example 5 film B5 0.8 60 0 17 * UV blocker content: parts by weight of solid content of UV blocker added per 100 parts by weight of PET resin

Preparation example of polyimide film

After filling 563.3 g of dimethylacetamide (DMAc) as an organic solvent in a nitrogen atmosphere at 20°C in a double-jacketed 1L glass reactor with temperature control, 2,2'-bis(trifluoromethyl)-4,4 '-Diaminophenyl (TFMB) and 4,4'-oxydianiline (ODA) were added and dissolved. Then, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6-FDA) was slowly added and stirred for 2 hours. Then, isophthaloyl chloride (IPC) was added and stirred for 2 hours, terephthaloyl chloride (TPC) was added and stirred for 3 hours to prepare a polymer solution.

After apply|coating the obtained polymer solution to a glass plate, it dried with hot air at 80 degreeC for 30 minutes. Thereafter, the dried gel sheet was fixed to the pin frame while being stretched 1.01 times in the first direction, and was fixed to the pin frame while being stretched 1.03 times in the second direction perpendicular to the first direction. Thereafter, the dried gel sheet was cured in an atmosphere in which the temperature was raised at a rate of 2° C./min in a temperature range of 80° C. to 300° C. while being fixed to the pin frame. Thereafter, a polyimide film having a thickness of 50 μm was obtained through a cooling step.

Modulus test example of laminated sheet

A specimen was prepared by cutting each of the first polyester, cover window, and second polyester film constituting the laminated sheet prepared above, and the modulus, that is, Young's modulus, was measured.

- Initial dimension in tension direction: 50 mm

- Dimensions in the direction perpendicular to the direction of tension: 15 mm

- Test temperature: room temperature (25℃)

- Test equipment: Instron's UTM 5566A

- Tensile speed: 50 mm/min

- Tensile direction: longitudinal (MD) or transverse (TD) direction

division Modulus (GPa) (25℃) first polyester film cover window 2nd polyester film MD TD MD TD MD TD sheet A1 Comparative Example 1 4.1 4.6 5.6 5.8 3.9 5.1 sheet A2 Comparative Example 2 3.9 4.5 5.8 5.7 4.1 4.6 sheet B1 Example 1 4.3 4.7 6.3 6.6 3.9 5.2 sheet B2 Example 2 4.1 4.6 5.9 6.1 4.0 5.1 sheet B3 Example 3 4.2 4.7 5.7 6.3 4.1 5.2 sheet B4 Example 4 4.3 4.8 6.9 6.7 3.9 5.2 sheet B5 Example 5 4.2 4.7 6.7 6.6 4.1 5.3

Folding properties after UV irradiation

After manufacturing a display module by attaching the laminated sheet prepared above on one surface of the display panel, a folding durability test was performed as shown in FIG. 4 after UV irradiation as follows.

(1) UV irradiation

- UV equipment: Q-lab's QUV Tester

- UV lamp: UVB-313

- UV dose: 0.66 W/m ² @310 nm

- UV total dose: 31.62 W/m ² @250-400 nm

- UV irradiation time: 24 hours

(2) Folding test

- Test equipment: Toyoseiki's MIT-D0A

- radius of curvature (R): 1.5 mm

- Folding test procedure: MIT folding test according to ASTM D 2176 and TAPPI T 511

- Criteria: If delamination, driving error, whitening, or other defects were confirmed after repeated folding for 200,000 times, X was set, and O was set if not confirmed.

The results are summarized in the table below.

division Folding Durability sheet A1 Comparative Example 1 X sheet A2 Comparative Example 2 X sheet B1 Example 1 O sheet B2 Example 2 O sheet B3 Example 3 O sheet B4 Example 4 O sheet B5 Example 5 O

As shown in the table above, the display module including sheets A1 or A2 had a defect during repeated folding of more than 200,000 times after UV irradiation, but the display module including sheets B1 to B5 had defects during repeated folding of more than 200,000 times after UV irradiation. Defects such as delamination, driving error, and whitening were not observed, confirming excellent UV durability and flexibility.

1: flexible display device;
1': organic light emitting display device,
1a: an in-folding type flexible display device,
1b: an out-folding type flexible display device,
2: test equipment
10: cover, 11: psalm,
20: display panel;
20-1: front polarizer, 20-2: organic light emitting display panel,
30: frame,
21: jig, 22: load cell,
100: polyester film, 101: specimen,
100a: front protection film, 100b: back protection film,
200: cover window, 300: adhesive layer;
A, A': cutting line, p1, p2: folding point,
R: curvature, w: spacing.

Claims (11)

transparent substrate;
a first polyester film disposed on one surface of the transparent substrate; and
A second polyester film disposed on the other surface of the transparent substrate,
The first polyester film is
(i) the UV blocking agent is included in an amount of 0.5 to 2.0 parts by weight based on 100 parts by weight of the polyester resin included in the first polyester film,
(ii) a total light transmittance of 2% to 5.5% for light having a wavelength of 370 nm;
(iii) a total light transmittance of 9.5% to 22% for light having a wavelength of 380 nm;
(iv) a total light transmittance of 65% to 85% for light having a wavelength of 390 nm, and
(v) has a total light transmittance of 85% to 95% with respect to light having a wavelength of 550 nm,
A laminated sheet, wherein the UV blocking agent is at least one compound having the structure of Formula 1 below:
[Formula 1]

in the above formula
R ₁ and R ₂ are each independently hydrogen, alkyl, or alkenyl,
L is a single bond or a hydrocarbon chain, hydrocarbon ring or heterocyclic ring having one or more unsaturated bonds.
The method of claim 1,
The content of the UV blocker in the second polyester film is less than 0.1 parts by weight relative to 100 parts by weight of the polyester resin included in the second polyester film, the laminated sheet.
The method of claim 1,
The weight reduction rate of the UV blocking agent is 15% or less after maintaining for 1 hour in an air atmosphere of 280°C under isothermal conditions of a thermogravimetric analyzer (TGA).
The method of claim 1,
A laminated sheet, wherein the laminated sheet satisfies the following formulas (1) and (2):
1.5 ≤ T1/T2 ... (1) 0.8 ≤ M2/M1 ≤ 1.2 ... (2)
in the above formula
T1 is the thickness of the first polyester film,
T2 is the thickness of the second polyester film,
M1 is the modulus (GPa) with respect to the width direction (TD) of the first polyester film,
M2 is the modulus (GPa) with respect to the width direction (TD) of the second polyester film.
delete delete The method of claim 1,
The first polyester film has a thickness of 20 μm to 80 μm,
The said 2nd polyester film has a thickness of 30 micrometers or less, The lamination sheet.
The method of claim 1,
The first polyester film,
A laminated sheet having a final tensile rate of 3% or less when irradiated with UV-B light for 24 hours and lasting for 1 hour with a load of N2% in the first direction in-plane:
Here, the N2% load is a load that stretches the film by 2% compared to the initial direction in the first direction, and the UV-B light has a peak wavelength within 310 nm to 315 nm, and is irradiated at a wavelength of 310 nm. ) is 0.66 W/m ² , and the total irradiation amount in the 250 nm to 400 nm wavelength band is 31.62 W/m ² .
The method of claim 1,
After irradiating the laminated sheet with UV-B light for 24 hours, the number of repeated folding under the condition of a curvature radius of 1.5 mm until delamination occurs is 200,000 times or more.
The method of claim 1,
The laminated sheet, wherein the transparent substrate is a transparent polyimide film or ultra-thin glass (UTG).
flexible display panel; and
A laminated sheet disposed on the flexible display panel,
The laminated sheet is
a transparent substrate disposed on the display panel;
a first polyester film disposed on the transparent substrate; and
A second polyester film disposed under the transparent substrate,
The first polyester film is
(i) the UV blocking agent is included in an amount of 0.5 to 2.0 parts by weight based on 100 parts by weight of the polyester resin included in the first polyester film,
(ii) a total light transmittance of 2% to 5.5% for light having a wavelength of 370 nm;
(iii) a total light transmittance of 9.5% to 22% for light having a wavelength of 380 nm;
(iv) a total light transmittance of 65% to 85% for light having a wavelength of 390 nm, and
(v) has a total light transmittance of 85% to 95% with respect to light having a wavelength of 550 nm,
The UV blocking agent is at least one compound having the structure of Formula 1 below, a flexible display device:
[Formula 1]

in the above formula
R ₁ and R ₂ are each independently hydrogen, alkyl, or alkenyl,
L is a single bond or a hydrocarbon chain, hydrocarbon ring or hetero ring having one or more unsaturated bonds.

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